/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.supply.dl.widget.adapter;

import android.os.Parcelable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.view.PagerAdapter;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;

/**
 * Implementation of {@link PagerAdapter} that
 * represents each page as a {@link Fragment} that is persistently
 * kept in the fragment manager as long as the user can return to the page.
 * <p>This version of the pager is best for use when there are a handful of
 * typically more static fragments to be paged through, such as a set of tabs.
 * The fragment of each page the user visits will be kept in memory, though its
 * view hierarchy may be destroyed when not visible.  This can result in using
 * a significant amount of memory since fragment instances can hold on to an
 * arbitrary amount of state.  For larger sets of pages, consider
 * {@link android.support.v4.app.FragmentStatePagerAdapter}.
 * <p>When using FragmentPagerAdapter the host ViewPager must have a
 * valid ID set.</p>
 * <p>Subclasses only need to implement {@link #getItem(int)}
 * and {@link #getCount()} to have a working adapter.
 * <p>Here is an example implementation of a pager containing fragments of
 * lists:
 * {@sample development/samples/Support4Demos/src/com/example/android/supportv4/app/FragmentPagerSupport.java
 * complete}
 * <p>The <code>R.layout.fragment_pager</code> resource of the top-level fragment is:
 * {@sample development/samples/Support4Demos/res/layout/fragment_pager.xml
 * complete}
 * <p>The <code>R.layout.fragment_pager_list</code> resource containing each
 * individual fragment's layout is:
 * {@sample development/samples/Support4Demos/res/layout/fragment_pager_list.xml
 * complete}
 */
public abstract class FragmentPagerAdapter extends PagerAdapter
{
	private static final String TAG = "FragmentPagerAdapter";
	private static final boolean DEBUG = false;

	private final FragmentManager mFragmentManager;
	private FragmentTransaction mCurTransaction = null;
	private Fragment mCurrentPrimaryItem = null;

	public FragmentPagerAdapter(FragmentManager fm)
	{
		mFragmentManager = fm;
	}

	private static String makeFragmentName(int viewId, long id)
	{
		return "android:switcher:" + viewId + ":" + id;
	}

	/**
	 * Return the Fragment associated with a specified position.
	 */
	public abstract Fragment getItem(int position);

	@Override
	public void startUpdate(ViewGroup container)
	{
	}

	@Override
	public Fragment instantiateItem(ViewGroup container, int position)
	{
		if (mCurTransaction == null)
		{
			mCurTransaction = mFragmentManager.beginTransaction();
		}

		final long itemId = getItemId(position);

		// Do we already have this fragment?
		String name = makeFragmentName(container.getId(), itemId);
		Fragment fragment = mFragmentManager.findFragmentByTag(name);
		if (fragment != null)
		{
			if (DEBUG)
				Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
//            mCurTransaction.attach(fragment);
			mCurTransaction.show(fragment);
		}
		else
		{
			fragment = getItem(position);
			if (DEBUG)
				Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
			mCurTransaction.add(container.getId(), fragment, name);
		}
		if (fragment != mCurrentPrimaryItem)
		{
			fragment.setMenuVisibility(false);
			fragment.setUserVisibleHint(false);
		}

		return fragment;
	}

	/**
	 * 根据下标。获取fragment对象
	 */
	public Fragment getFragment(ViewGroup container, int position)
	{
		final long itemId = getItemId(position);
		String name = makeFragmentName(container.getId(), itemId);

		return mFragmentManager.findFragmentByTag(name);
	}

	@Override
	public void destroyItem(ViewGroup container, int position, Object object)
	{
		if (mCurTransaction == null)
		{
			mCurTransaction = mFragmentManager.beginTransaction();
		}
		Fragment fragment = (Fragment) object;
		if (DEBUG)
			Log.v(TAG, "Detaching item #" + getItemId(position) + ": f=" + object
					+ " v=" + (fragment).getView());
		mCurTransaction.hide(fragment);
	}

	@Override
	public void setPrimaryItem(ViewGroup container, int position, Object object)
	{
		Fragment fragment = (Fragment) object;
		if (fragment != mCurrentPrimaryItem)
		{
			if (mCurrentPrimaryItem != null)
			{
				mCurrentPrimaryItem.setMenuVisibility(false);
				mCurrentPrimaryItem.setUserVisibleHint(false);
			}
			if (fragment != null)
			{
				fragment.setMenuVisibility(true);
				fragment.setUserVisibleHint(true);
			}
			mCurrentPrimaryItem = fragment;
		}
	}

	@Override
	public void finishUpdate(ViewGroup container)
	{
		if (mCurTransaction != null)
		{
			mCurTransaction.commitAllowingStateLoss();
			mCurTransaction = null;
			mFragmentManager.executePendingTransactions();
		}
	}

	@Override
	public boolean isViewFromObject(View view, Object object)
	{
		return ((Fragment) object).getView() == view;
	}

	@Override
	public Parcelable saveState()
	{
		return null;
	}

	@Override
	public void restoreState(Parcelable state, ClassLoader loader)
	{
	}

	/**
	 * Return a unique identifier for the item at the given position.
	 * <p>The default implementation returns the given position.
	 * Subclasses should override this method if the positions of items can change.</p>
	 * @param position Position within this adapter
	 * @return Unique identifier for the item at position
	 */
	public long getItemId(int position)
	{
		return position;
	}
}
